declare
  @myappuserid uniqueidentifier = newid()
 ,@now datetime = getdate()
 ,@aspnetdb_username nvarchar(max) = 'josephstyons'
 ;

INSERT INTO APPUSER(
  ID
 ,ASPNETDB_USERID
 ,DATEADDED
 ,DATECHANGED
 ,ADDEDBYID
 ,CHANGEDBYID
)
select
  @myappuserid
 ,userid
 ,@now
 ,@now
 ,@myappuserid
 ,@myappuserid
from
  sep_aspnetdb.dbo.aspnet_users
where username = @aspnetdb_username

select
  netu.UserName
 ,au.*
from
  sep.dbo.appuser au
  inner join
  sep_aspnetdb.dbo.aspnet_users netu
  on netu.UserId = au.ASPNETDB_USERID